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(Barely) passed SCJD with 344/400

 
Björn Wessman
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General Considerations (maximum = 100): 90
Documentation (maximum = 70): 69
O-O Design (maximum = 30): 30
GUI (maximum = 40): 31
Locking (maximum = 80): 44
Data store (maximum = 40): 40
Network server (maximum = 40): 40

It would have been interesting to know what the points in the GUI section were drawn from. I was quite pleased with the GUI from a usability point of view, but perhaps it was something technical...
But more than anything, what did I do wrong with the locking? It must have been something essential when I only get half of the maximum score. But I actually made a test app where I ran 100 concurrent threads without any problems, so I'm a bit confused here... It would have been nice to know for future projects what I did wrong.

But still, with only three weeks of puttin' in work, I didn't expect a perfect score so I guess I'm reasonably pleased with passing

Thanks for the help I got here!
 
K. Tsang
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Congrats.

My locking score is like yours but all my other sections are near full marks. My GUI score was like 39 and gen consideration 99, I really didn't know why that 1 point got deducted.

Back to locking, everyone knows we need locking to work. So as long it works (doesn't deadlock) we are happy. The remaining points are definitely on your design other than OO design. Probably algorithms and stuff.
 
Roberto Perillo
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Howdy, champ!

First, congratulations for the achievement!

Now, about the locking mechanism, it's sort of hard to tell what could possibly be wrong in your structure, but apparently some people get 44 in this section because it won't work in all cases... maybe it could be that you are not verifying if the record is still valid after acquiring its lock... maybe you are doing this check, but it could also be something like this... there are some tests I created for the locking mechanism (you can find them here), maybe you could try running it a couple of times to see if your application hangs at some point... or maybe it won't hang, but it could be that a client is overriding another client's data...

Anyway, congratulations again!!!
 
Anne Crace
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The dreaded 44/80 on locking is a big mystery around here Since they don't give you an explanation as to why you lost points, I guess it will always be a mystery. But you should be glad you passed, and with a minimal effort as far as time spent. I think passing SCJD with 3 weeks of work is fantastic! Congrats.
 
Roel De Nijs
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Hi Bjorn,

Congratulations! A pass is a pass

About the locking score: there is even a thread about this mistery score of 44/80, you can find it here. Some questions about your locking strategy:
  • how did you handle a client (holding already a lock) requesting a lock on that same record
  • how did you handle a client (holding already a lock) requesting a lock on another record
  • did you check your test-app not resulted in overwriting data (like Roberto already said)

  • To be sure my locking mechanism didn't allow overwriting I had a test case launching 35 threads and each thread booked exactly 1 room and at the end there were always 4 threads without a room (so the unlucky ones had to sleep on the streets instead of a nice hotel room ) and if I checked the file every room was booked by 1 thread.

    And I think Anne (and many others, like me) would be jealous about you spending just 3 weeks on it, because she is working on a 3 year plan . But just 3 weeks is really, really fast. Maybe you can get a place in the Guiness Book of World Records for this achievement

    Kind regards,
    Roel
     
    Gert-Jan den Besten
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    Wow...... I think passing the SCJD exam with an 86% score with only 3 weeks of work is awesome
     
    Björn Wessman
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    Thanks for the suggestions about the locking score, I will look into it.

    About the development time: I did spend eight hours a day for those three weeks, so it's still 120 hours. I also read Monkhouse's book which I didn't include in those three weeks. That book + this forum + some assistance from a friend who already passed the SCJD helped me a lot.
     
    K. Tsang
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    Now I found the 44/80 locking score a very interesting mystery to solve. I found previously people can get 65 and now 44.

    The 65 score thread here

    Does it really make a different in using a hash table, map, set as the collection for storing locked records??
     
    Andrew Monkhouse
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    Congratulations. A pass is a pass, and you can now say that you are a qualified SCJD!
     
    Bert Bates
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    congrats, and off to the results forum!
     
    Cameron Wallace McKenzie
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    Congratulations!


    -Cameron McKenzie
     
    Matheus Mendes
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    Congratulations Wessman !

    Really 3 weeks it's a pretty short time, I spent around one year and I just submitted my project on the last friday and I yet must do the essay exam. Hope soon to create a topic as yours Wessman !

    The test suit made by perillo is very useful, It helped me to fix a lot of problems, specially with deadlock .

    Best regards !
     
    Vijitha Kumara
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    Congrats

     
    With a little knowledge, a cast iron skillet is non-stick and lasts a lifetime.
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